Light Emitting Diode (LED), also known as luminous diode, is regarded as the fourth generation of light source to replace traditional incandescent lamp, fluorescent lamp and high intensity discharge lamp, because it is energy-saving, environment-friendly, safe, reliable, instant in starting and long in service life.
At present, there are mainly two ways of generating white light with LED lamps as follows:
The first way is generating white light through combination three LED chips of red light, green light and blue light;
The second way is generating white light by using LED chip of blue light, or combination of LED chips of blue light and red light, together with fluorescent cover made by yellow fluorescent powder and transparent colloid.
The second way is widely used to emit light at present; however, there are defects as follows: the technique of shaping the fluorescent cover using mixture of transparent colloid and fluorescent powder is complex, high in cost, non-uniform in heat conduction and light emitting, and bad in high temperature resistance; and it cannot guarantee uniformity of the mixed materials.
Some existing techniques produce LED fluorescent covers by adopting mixture of liquid epoxy resin or liquid silicone rubber with fluorescent powder, and covering the mixture onto the LED chip on the LED bracket with dispenser. For example, the Chinese patent application with an application number of 201310064846.7 disclosed an LED fluorescent lamp cover, using liquid epoxy resin or liquid silicone rubber as base stock, with yellow fluorescent powder as stuffing, forming the raw material of fluorescent lamp cover at a proportion of adding 0.3-10 weight parts of yellow fluorescent powder into 100 weight parts of base stock, and then obtaining the fluorescent lamp cover of required shape after injection molding, curing and mold release. The grain size of the fluorescent powder grain is 5-25 um. And the epoxy resin is bisphenol A epoxy resin.
However, because of using the liquid epoxy resin or liquid silicone rubber as base stock, the above technique is troublesome, and the fluorescent powder is easy to precipitate unevenly and the efficiency is low.
Another Chinese patent application with an application number of 201010586506.7 disclosed a preparation method of LED component, comprising steps of: 1) crystallizing chips in a support in a solid manner, leading wires to form electrodes; 2) mixing fluorescent powder with adhesive higher in viscosity in adhesive of bi-component silica gel to form fluorescent powder adhesive, defoaming the fluorescent powder adhesive to obtain defoamed fluorescent powder adhesive, mixing the defoamed fluorescent powder adhesive with adhesive lower in viscosity in the adhesive of the bi-component silica gel to form mixed adhesive, encapsulating the chips in the step 1) with the mixed adhesive and solidifying the silica gel to obtain the LED component. Because viscosity of the normal bi-component addition type silica gel is 2000-6000 cps, the fluorescent powder is easy to subside in the silica gel system if the grain size of the fluorescent powder is too big or the viscosity of the silica gel is low, it needs to be used within half an hour generally. If the mixing time is too long, the fluorescent powder subsides, which directly influences the optical coherence after encapsulation, namely the color temperature consistency and brightness consistency and so on.
Another Chinese patent application with an application number of 201310430400.1 disclosed a high thixotropic LED jelly glue preventing deposition of fluorescent powder, which by means of preferred coupling agent and optimized hydrolysis condition, modifies fumed silica to obtain thixotropic material, and modifies fluorescent powder to obtain anti-deposition fluorescent powder. The thixotropic material is added into the silica gel system to obtain a high thixotropic silica gel system with a high thixotropic index up to 5; jelly glues of different color temperature can be made integratively by adding different amount and different kinds of modified fluorescent powder into the system, the jelly glues will not deposit within the expiration date of 3 months, and the color temperature value does not change after encapsulation. The inventive jelly glue is packaged in cylinder and can be used directly on the dispenser without need of any mould, and it shapes automatically after dispensing.
The above techniques adopt high thixotropic single-component silica gel and modified fluorescent powder, manufacturing of the jelly glue involves many raw materials, and the process is very complex.